Okay for the peeps confused. There are TWO TIMELINES!!! ML went back in time, probably using her regret pill. So he has memories of MC that she does not have of him. He did it to make sure they never meet, because all he did in the last life was cause her pain. That's how he knows she's a mermaid, and why there's so many weird scenes about her being really mean when it seems like they've never met before, it's because she doesn't remember it, it was in a different timeline!
Okay for the peeps confused. There are TWO TIMELINES!!! ML went back in time, probably using her regret pill. So he has memories of MC that she does not have of him. He did it to make sure they never meet, because all he did in the last life was cause her pain. That's how he knows she's a mermaid, and why there's so many weird scenes about her being really mean when it seems like they've never met before, it's because she doesn't remember it, it was in a different timeline!